1. Field of the Invention
The present invention relates to a spring motor mechanism, and in particular, to a spring, motor mechanism for use in a child's swing having an adjustable swing height control mechanism, an over-wind protection device, and a remaining swing run indicator device.
2. Description of the Related Art
Spring motor mechanisms are well known and subject to various applications, however, they are especially suited for use in a child's swing and will therefore be particularly described in that connection. Child swings are often powered by a torsion spring, typically formed from wire, that receives and stores an input torque when wound by an operator through use of a handle linked to a crank shaft. The handle and crankshaft are typically located at the "escapement end" of the device, controls the release of the torque stored in the spring to sustain a decreasing, periodic oscillation that drives a swing seat containing a child.
Springs used in known spring motor mechanisms typically include a plurality of coils. As the spring is wound, the number of these coils increases while the diameter of each coil decreases. In this way, the length of the spring grows while its diameter shrinks. Springs often have coils within coils in a "telescope" fashion to allow room for additional coils within a limited space.
The energy generated during winding is stored in the spring, and this energy is released as the spring unwinds to oscillate the swing. The stored energy will continue to be released as the added spring coils unwind. Accordingly, for purposes of swing duration, it is the number of additional coils created during winding that is significant rather than the actual amount of torque that has been stored in the spring.
Spring motor mechanisms driven by wound torsion springs suitable for use in a child's swing are previously known and have been disclosed, for example, in U.S. Pat. Nos. 4,165,872 to Saint and 5,083,773 to Saint, among others. In the known device, the torsion spring is wound to create a torque that acts upon a ratchet wheel and a carriage thereby causing the swing, which is attached to the carriage, to oscillate.
In the known mechanism, the winding end of the device includes a handle and crankshaft structure as discussed above. The crank shaft is directly connected to the spring so that the rotation of the handle and crankshaft winds the spring. As discussed above, the rotational force applied to the spring by the rotating handle tightens the spring coils causing the coils to shrink in diameter. Eventually, with over winding, the wire spring will deform plastically, possibly damaging the torsion spring. Thus, a first disadvantage with known spring motor mechanisms is that the spring may become damaged if it is overwound by the operator.
Of course, repeated over winding of the spring can place substantial stress and strain on the main spring. If the main spring should inadvertently become disengaged with either the wind end or the escapement end, or if the main spring breads, the spring could begin to unwind rapidly, and generate an alarming sound.
Conventional spring motor mechanism unwind quickly and suffer from the disadvantage of failing to function for extended periods of time before requiring additional winding. Because the conventional spring motor mechanism is contained within a housing, the user cannot determine how tightly the spring is wound. Conventional spring motor mechanism do not provide the operator with an indication of the number of swing oscillations that can be completed before the spring must be rewound (i.e., the amount of stored energy remaininig in the spring).
Another disadvantage of conventional spring motor mechanisms relates to the nonlinear release of energy form the spring over time as the child swinigs. Specifically as the conventional spring motor mechanism first begins to unwind, the spring mechanism generates a relatively high torque output which swings the child very high. As the spring mechanism unwinds, the torque generated decreases, and the child swing decreases in amplitude. Consequently known spring motor mechanisms can over swing the child as the spring initially unwinds and under swing the child as the springs finishes unwinding.
Known spring motor mechanisms also do not account for variations in the child's weight. Thus, a conventional spring motor mechanism that supplies sufficient torque to appropriately swing a larger heavier child tends to over-swing a smaller lighter child.